1. Field of the Invention
The present invention relates to a method and an apparatus for recording an image, and more particularly to a method and an apparatus for recording an image on a multicolor thermal recording material.
2. Description of the Related Art
At present, a thermal recording method is known as a method of recording an image on recording paper by using heating elements. In this thermal recording method, recording is effected by a process in which, by using a thermal recording material in which a base such as paper or synthetic paper is coated with a coupler and a developer, the thermal recording material is subjected to heat processing by means of a thermal head. For instance, a technique has been proposed wherein a thermal recording material, in which a plurality of electron-donating dye precursors and electron-receiving compounds are present in mixed form, is prepared, and heat of different temperatures is applied to the recording material by making use of the fact that color-development starting temperatures differ for the respective electron-donating dye precursors, so as to obtain an image having different hues (Japanese Patent Application Publication No. 69/1974). Such a thermal recording method has advantages in that (1) development is not required, (2) in a case where the base is paper, the paper quality is close to that of plain paper, (3) handling is easy, (4) the color-development density is high, (5) the recording apparatus is simple and inexpensive, and (6) the noise occurring during recording is smaller than in the case of a dot printer or the like. Hence, this thermal recording method has disseminated rapidly in recent years in the fields of black-and-white facsimile machines and printers.
In these fields of recording, in conjunction with rapid development made in the information industry, there has been a demand for obtaining color hard copies simply from terminals of information equipment including computers and facsimile machines.
A digital color printer is known as a printer which meets this demand. In this digital color printer, a color image is separated into the image data of yellow (Y), magenta (M), cyan (C), and black (K) with respect to the color components, and the image is recorded in each corresponding thermosensitive layer on the basis of the image data of each color.
In addition, in a case where characters are recorded on an image, character data is sometimes inputted separately so as to effect recording in such a manner as to facilitate the discrimination between the image and the characters.
The preparation of the above-described thermosensitive material having thermosensitive layers corresponding to the respective colors is complicated in production, and the production costs are high. Hence, there has been a demand for a method of recording an image on a thermosensitive material of three colors, Y, M and C.
However, in a case where a black image and characters are recorded on the multicolor thermal recording paper by the combination of the three colors of Y, M and C, as described above, densities of the color components of the black color are close to those of a color image and, hence, lacked a sharp contrast. For this reason, if the characters and the color image are recorded on the same image plane, the separation between the characters and the image is poor, which presents the problem that the discrimination of the characters is difficult.
In addition, thermal recording materials are known on which an image is recorded as light beams of different wavelength regions are applied thereto. Such thermal recording materials which have been proposed for use as photosensitive materials include, among others, the following: one in which two components of a two-component-type thermosensitive color-development medium are disposed by being separated from each other via microcapsules containing a photo-curing composition (Japanese Patent Application Laid-Open No. 89915/1977); one in which a layer containing a photopolymerizing composition and a vinyl monomer having an acidic group, an isolating layer, and a layer consisting of an electron-donating colorless dye are laminated (Japanese Patent Application Laid-Open No. 123838/1986); and one provided with a plurality of photosensitive layers which produce different colors, each photosensitive layer having a central wavelength (Japanese Patent Application Laid-Open Nos. 224930/1989 and 19710/1990). According to these techniques, as light beams of different ultraviolet wavelength regions corresponding to an image to be recorded are applied to the thermal recording material, the development of hues corresponding to the areas irradiated with the light beams and the wavelength regions of the light beams is suppressed. Then, as the thermal recording material is subjected to heating, the thermal recording material undergoes heat development in areas where the light beams were not applied, thereby forming an image.
Even if these photosensitive-type thermal recording materials are used, a problem similar to that described above is encountered.
In addition, the present inventors have proposed multicolor thermal recording materials which are provided with substantially transparent color-development layers adapted to develop different hues of color, and which make it possible to obtain an unprecedentedly excellent heatsensitized, color-developed image (Japanese Patent Application Laid-Open Nos. 288688/1991 and 28585/1992). With respect to each of these thermal recording materials, a thermal head arrayed in the main-scanning direction is moved in the sub-scanning direction to effect scanning, thereby to record an image.
According to these techniques, it is possible to obtain multicolor images with excellent hues, color separability, and image preservability, which have hitherto been impossible to obtain with the thermal recording system. In addition, it is possible to render the obtained image into a transmitted image or a reflected image.
With such thermal recording paper, in a case where a multiplicity of color-development layers are provided in a superposed state on one surface thereof, it is necessary to cause the heating and color development of an uppermost layer (a layer closest to the surface) with a quantity of heat which does not heat the other layers. Then, after completion of the fixation processing of this color-development layer, it is necessary to perform heat processing of the remaining color-development layers.
As shown in FIG. 18, the duration of this fixation processing (nth time) includes both a duration for effecting the fixing of unnecessary color-development components for suppressing the color development of each color-development layer, and a duration for effecting uncoloration so as to prevent a change with time and the coloring of the texture. Conventionally, it was necessary to wait for the heat processing ((n+1)th time) of an ensuing color-development layer until the aforementioned two processes are completed.
With such an image recording method, however, there are limits to the reduction of a total recording period. If an attempt is made to effect recording by exceeding a limit, the duration for effecting uncoloration becomes insufficient due to a shortage of the amount of light. With the lapse of time, this can possibly cause coloration of a white frame portion surrounding the image, in particular.
For this reason, it is conceivable to increase a unit amount of light of a light source, but since the quantity of heat generated in the light source increases, this measure is not suitable for thermal recording materials.
Furthermore, picture elements which are not to be made to undergo color development are sometimes present in an image. For instance, there is no need to cause color development in the frame portion surrounding the image.
No heat is applied to those picture elements whose indicated density based on an image signal is 0, and a difference occurs in the luster as between a portion to which heat has been applied and a portion to which it has not. The difference in luster results in an unnatural image, so that there is the problem that it is impossible to reproduce a proper image based on the image signal.
To overcome this problem, it is conceivable to provide an arrangement in which, by providing a heat roller downstream in a traveling direction of the thermal recording paper, the overall surface of the thermal recording paper is subjected to heat processing with a predetermined amount of energy by this heat roller after completion of the heat processing of all the color-development layers.
Consequently, it is possible to make the luster uniform, improve the reproducibility of the image, and overcome the unnaturalness of the image.
With such an image recording method, however, since the duration for heating the overall surface by the heat roller is added to the duration for the heat processing of the respective color-development layers, the overall recording period becomes disadvantageously prolonged.